title: Femoral sizing in total knee arthroplasty is rotation dependant.
abstract: OBJECTIVE
  The mismatch between the medio-lateral (ML) and the antero-posterior (AP) size of femoral components in total knee arthroplasty (TKA) has been linked to gender, ethnicity, morphotype and height differences in patients. The hypothesis of this study was that the AP size measurement of a femoral component increases with more external rotation in posterior referencing TKA.
  
  
  METHODS
  During a 2-year period, 201 patients were included in this prospective study. The AP distance of the distal femur was measured with an AP sizer of the Vanguard (Biomet, Warsaw, US) knee system. This AP sizer allows to dial in external rotation by 1° increments and to determine the femoral size with an anterior boom. AP size was noted at 0°, 3° and 5° of external rotation and then compared for ML matching.
  
  
  RESULTS
  Antero-posterior and corresponding ML sizes match perfectly for the Vanguard at 0° of external rotation and a central boom position on the anterior femoral surface. Then, the anterior boom was positioned on the antero-lateral cortex and the AP size increased a mean (SD) 1 (0.5) mm. With 3° of external rotation, the AP size increased a mean (SD) 2.3 (0.4) mm and for 5° a mean (SD) 3.8 (0.3) mm (P < 0.05). This increase in AP size resulted in ML overhang of 2.2 (1.2) mm for 3° and 4.8 (2.6) mm for 5° (P < 0.05).
  
  
  CONCLUSIONS
  Antero-posterior size measurement of the distal femur is determined by the anatomy of the anterior surface with a higher antero-lateral cortex and the amount of external rotation that is dialled in during surgery. Since these parameters vary case per case, the availability of narrow components offers more surgical options to the surgeon and its importance extends beyond the gender aspect allowing different amounts of external rotation to be used without ML overhang.
  
  
  METHODS
  II.
authors.affiliation: Department of Orthopedic Surgery, Cliniques Universitaires Saint Luc, Avenue Hippocrate 10, 1200, Brussels, Belgium.
authors.forename: Angelique
authors.initials: A
authors.lastname: Koninckx
authors.forename: Arnaud
authors.initials: A
authors.lastname: Deltour
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Thienpont
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D001837:Body Weights and Measures; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000601:surgery*; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D011446:Prospective Studies; D012399:Rotation; D012737:Sex Factors